1. Field of the Invention
The invention relates to a redetachable, self-adhesive device which can be released again from its adhesive bond without leaving any residue by pulling on the adhesive film arranged on it.
2. Description of Related Art
Such devices, in particular hooks, are known. For instance, DE 42 33 872 C2 describes a redetachable, self-adhesive hook which is equipped with an adhesive film which can be adhesively released by pulling and which is commercially available as "tesa.RTM. Power-Strips with Hooks". A so-called system hook with base plate and attachable decorative hook is also commercially available as the "tesa.RTM. Power-Strip System Hook".
WO 94/21157 also discloses such a hook, which differs from the abovementioned hook in particular by the use of an adhesive film of the kind which is highly extensible and at the same time does not recover its original form.
In the practical use of such devices, problems may occur, however, in particular during later detachment. This is so since a re-releasable adhesive bond is achieved in all the abovementioned cases by a stretching of the self-adhesive tape used for the adhesive bonding and provided on one or both sides with a contact adhesive. For this purpose, starting from a grip, the adhesive tape is pulled in the direction of the grip substantially parallel to the bonding plane. The extension of the adhesive tape which is produced causes it to be released from the underlying surface without leaving any residue. WO 92/11332, WO 92/11333, WO 94/21157 and WO 95/06691 specify as the maximum pulling-off angle for redetachment without leaving any residue an angle of 35.degree. between the bonding plane and the extending direction. In addition to high extensibility, a low offset yield stress in the case of low to moderate extensions combined with an adequately high tearing resistance in the case of high extensions are important for releasing the adhesive tape from an adhesive joint completely and without leaving any residue. For a reliable detachment process, the tearing resistance must in this case be well above the force which is necessary for releasing the adhesive tape from the adhesive joint (stripping force). If the stripping force is greater than the tearing resistance of the adhesive tape, the adhesive tape tears during the releasing process.
Interesting applications of previously described self-adhesive tapes comprise, inter alia, use in adhesive hooks, such as are frequently used domestically in bathrooms and kitchens (see DE 42 33 872, WO 94/21157, U.S. Pat. No. 5,507,464) or else specific adapter systems. Commercially available in this respect are, inter alia, adhesive hooks of modular construction (tesa Power-Strips System Hooks), comprising a base plate to which the hook body is adapted. Corresponding base plates thereby allow mouldings of the widest variety of formations to be adapted, permitting a wide range of variations of applications. Examples comprise adapters for the fixing of cables, mirrors, pictures etc.
What is disadvantageous about the previously known problem solutions is that the releasing of the adhesive bond has to take place by pulling the adhesive strips substantially in the bonding plane. Errors in use are consequently inevitable for the inexperienced user. If the adhesive tape is pulled off at a significant angle with respect to the bonding plane or even perpendicularly forwards, the additionally occurring frictional forces and the additional contact pressure between the adhesive tape and the object to which it is adhesively bonded, or the base plate used, may cause tearing of the adhesive tape in the region of the pulling-off edge of the adhesive film. The tearing resistance relevant here is not identical to that determined in accordance with DIN 53504 in the tearing force/ultimate elongation experiment. Rather, owing to the pulling out of the adhesive films from the adhesive joint at an angle other than 0.degree., it is at usually considerably lower values. Increasing the tearing resistances of the adhesive tapes used is one possible way of reducing the tendency to tear. However, a corresponding measure is often only possible to a limited extent, since it (for example the use of thicker self-adhesive tapes or more tear-resistant intermediate substrates) cannot be carried out selectively without adversely influencing other product properties, such as for example the extensibility.
Tearing of the adhesive tape may likewise occur if the stretching of the adhesive tape is performed, as intended, substantially in the plane of the adhesive bond and in the direction of the grip. In many case it has been found that tears are caused in this case by the user exerting very considerable force to press the item to be released perpendicularly against the object to which it is adhesively bonded during the releasing process. As a result of this also, the force necessary for pulling the adhesive tape out of the adhesive joint is increased to such a great extent that the tearing resistance is exceeded, with the unfortunate consequence for the user that the adhesive tape tears and the adhesive bond can no longer be released non-destructively and without leaving any residue.
And finally there are many applications in which, for reasons of spatial limits, pulling in the direction of the bonding plane is not possible, for instance because the adhesive bonding was performed in a depression or in a corner.
The object of the present invention was to overcome the aforementioned disadvantages.